Many attempts have been made to provide absorbent products, such as disposable diapers, sanitary napkins, and incontinent pads which are used to absorb and to contain body fluids. Most of such products contain an absorbent batt which is placed between a liquid-impermeable backing and a liquid-permeable facing. In both the infant diaper and adult incontinent product product marketplace, a product is needed which has a large storage capacity. In this connection, copending U.S. patent applications Ser. Nos. 535,193 and 626,167 disclose a disposable pad which comprises a liquid-impermeable, substantially flexible shell preferably thermoformed from an ethylene-containing polymer foam, said shell containing a superstructure capable of maintaining void volume when wet and an absorbent medium. The shell generally has a boat-like shape and ranges in thickness from about 1/64 inch to about 1/4 inch. The shell has a length which ranges from about 4 inches to about 12 inches, a width measured from one rim to another across the top space from about 2 inches to about 7 inches, and a depth measured from a line extending across the width of the upper shell rim in the central portion from about 0.125 to about 2.5 inches. Adhesive lines are applied on the underside of the shell to provide the securement means for securing the pad to the clothing of the user. These adhesive lines are covered with release strips which when peeled from the adhesive strips leave the adhesive tacky.
Polyethylene film is a well known release surface for pressure sensitive adhesives, and thus it is clear that an extremely aggressive adhesive is necessary in order to provide a strong adhesion level to polyethylene film. It is even more difficult to obtain a strong adhesion level to polyethylene-containing foams. A common practice is to transfer coat a non-supported pressure-sensitive adhesive on a silicone liner to polyethylene film. When it was attempted to carry out a similar procedure in order to transfer coat a non-supported pressure-sensitive adhesive to polyethylene-containing foam, the resultant adhesive bond completely failed.
It must also be borne in mind that adhesive in a hot-melt state cannot be applied to foam in view of the fact that the foam is far too heat sensitive. Therefore, the desirable pressure-sensitive adhesive must be applied in the cold state. It is also impractical to use solvents for applying the adhesives, since massive ovens would be needed for removing the solvents. Many attempts have been made at improving the pressure-sensitive adhesive anchorage to ethylene-containing polymer foams via Corona or Flame treatment of the foam as well as by using various primers to enhance the bond, but none of these approaches has been completely adequate.
Surprisingly, it was found that when an adhesive of the same formulation as above, was coated on a reinforcing inner substrate having a non-recoverable extensibility of less than 100%, then said adhesive performed well on the foam backing.
In accordance with a preferred embodiment of the present invention, a thermoplastic rubber adhesive which is highly loaded with solid tackifying resin provides the desired bond to an ethylene-containing polymer foam surface, even without Corona, Flame or primer treatment. Said adhesive provides an adhesion to steel exceeding 120 oz/inch width.
It has been attempted, in the past, to utilize "double-faced" pressure-sensitive adhesive tape for securing a polyethylene film backing to the clothing of the user. Such double-faced tape consists of a thin, film-like substrate having adhesive coatings applied to each surface. When "standard" double-faced tapes are utilized for adhering to an ethylene-containing polymer foam backing, such tapes fail to satisfactorily perform their intended function. When the release strip is removed, it has the effect of delaminating the foam backing or pulling the adhesive completely away from the foam, rather than being cleanly released. This problem is overcome, in accordance with the present invention. Of course, the adhesive level of the double-faced tape attached to the undergarment must desirably be less than the adhesive level of the side of the double-faced tape attached to the ethylene-containing polymer foam backing, so as to permit the easy removal of the backing from the undergarment. This can be accomplished, either by reducing the adhesive level of the side of the double-faced tape attached to the undergarment, as compared to the opposite face of the tape, or, if the formulation of the adhesive is the same on both sides of the double-faced tape, then the adhesive level of one side may be reduced by covering part of the adhesive on said one side with a strip of non-adhesive material, or by omitting part of the adhesive on said one side.